We investigate the velocity dispersion of Pal 14 , an outer Milky-Way globular cluster at Galactocentric distance of 71 kpc with a very low stellar density ( central density 0.1- 0.2 \mbox { $ { M } _ { \odot } $ } /pc ^ { 3 } ) .
Due to this low stellar density the binary population of Pal 14 is likely to be close to the primordial binary population . Artificial clusters are generated with the observed properties of Pal 14 and the velocity dispersion within these clusters is measured as Jordi et al .
( 12 ) have done with 17 observed stars of Pal 14 .
We discuss the effect of the binary population on these measurements and find that the small velocity dispersion of 0.38 km/s which has been found by Jordi et al .
( 12 ) would imply a binary fraction of less than 0.1 , even though from the stellar density of Pal 14 we would expect a binary fraction of more than 0.5 .
We also discuss the effect of mass segregation on the velocity dispersion as possible explanation for this discrepancy , but find that it would increase the velocity dispersion further . Thus , either Pal 14 has a very unusual stellar population and its birth process was significantly different than we see in today ’ s star forming regions , or the binary population is regular and we would have to correct the observed 0.38 km/s for binarity .
In this case the true velocity dispersion of Pal 14 would be much smaller than this value and the cluster would have to be considered as “ kinematically frigid ” , thereby possibly posing a challenge for Newtonian dynamics but in the opposite sense to MOND .